Power fuse



Oct. 21, 1947. w. D. KYLE, JR., l-:T AL

POWER FUSE Filed April l5, 1943 wu L/Am ZJ. m45, J.

im m1 U. M m N H vthe operative condition of Patented Oct. 21, 1947UNITED PATENT? orrlc PowER Yan Ryan. Southy .Kyle Qomorotlon, South D.lygle Je Milwinulree, and Anthony Milwaukee, Wis., assignorstocrporationofwisconsln Application. laprifl` 15, 1943,'541152414No,248,31559 `2 1 claim.' (otono-11o) -power fuse in which isoavoided-:the characteristic .deoiences of .conventional liquid fuses, `andwherein the :fuse housing frequiresno liquid-tight seals.

tusewhich While obo Another .object isz-to devise a powerv will quicklyiinterrtipt.y a. fheavycurrent Yrioting all .-possibilityof .a leakage:path 4of ,conse- .quential A-pr@portions being established :followinga. luseoperation.

Still afnotherobjeot isA to provide afpowerY vfuse which cani readily-be`determined` by visual -inspectiom without Ydisvrnentling.

A further object is to K `which can easily be rehabilitated in the fieldat va cost which iscbut'o fraction pfthat-of ain entire 4fuse assembly.

-An additional Aobject is 'to devise a power fuse which will-Iblowwithout an accompainyingyiolent explosion sind, therefore,z willneither brustnor produce an objectionably 'loud report,v norgive oilobjectionable :fumes or become Lhot Qn being left r`inthe circuit,

One lembodiment ofpour invention is depicted in lthe -drawing,-wherein,:

Fig. g1 is a long itudinalsectional View of @cornplete fuse assembly,exclusive of the ln'iounting structure therefor i,

Fig. 2 is a longitudinal sectional yiew ora fuse insert or cartridgeconstituting a. replaceable component of the fuse assembly `aconstituent part of the inse-111311;

Fig- 3 is. en elevational view, of ,the -fuse assembly, drawn to a.smaller scale than Fig. 1;

Fig. ,4 is a cross-Sectional View tglren vatlorvig provideV a ,powerAfuse Vtue or .which the enclosed e4 fusedl T,tridee or. rinsert 2together withal helioalfretrect:

Fie. 6 isf .cross-,sectional Ylew .teken et ,liuc The entire ,fuse.esoembls es shownA eechoi ,Figo l endY 3 kiso self-.contained unitadopted. ,to be withdrewebly mounted er1-,ev suitable support.,

not shown, .having the.' .11511.31 ,line ilcrmrlalslld spring '.clinsorother .attachment moons by Arir- ,assembly ncon ycoolly eine quicklyvvloe mounted. Fusomounts oi vthatruit-.lire :being thorouehlyifamiliarto those who arecon- .cerneolwiththis ort, it lthought unnecessary toillustrate ce exeiriple thereof in .the presenteey111ication.

` 'lillel fuse shown includes. e. housing l in kwhich k ecorriprising oinse, cerf :ine spring and vci flexible .conductor 4 which ,shoots thespring and -isfcooriected at its lower end to the-.fuse cartridge .and.anchored .at its upper extremitytov the housing.

The housing Acomprises .e treusoarentfigloss. or .transparent yplalsticvtube 5j. fior exemple, Luoite ,which-.is mane `loog enough, et1east..;to.sccuf.e the requisite spacing between its metehooooed endswhereby to kensure..eetlust.eroine-oro: fol-lowing la, 4use blowout..Attached to the upper end Aof .tube L5 is1 e metY ferrule flffthis.being firmly se,- curel to the tube bycement or fusible metal, asiooicoted et L Ferrule lois designed -to.,.e.neage suitable ,terminalclips,f not shown, by means. of which the fusefelssemblyis-mounted1 Tlieder 'sien of this ierrule, es well the lower .ferrulo to. be, .describedflater, is. of course. adaptable to accommodate whatever vstyle ofmounting it kmet buttonfllke member .Il which, .forms the -llDRerterminal of the ooniprisixig parte@ .Lond .4. in avidi-tion to otherports ,de- `scribedhe.reiueiter.

To theflower .enclfofiubeis secured a second v1;f ;,ete.l .forrule ll..This-.is designedtoocoommodetearmounting `.clio` and threaded,externally @t .L4 ,to receive ,a remoxablecap t5, a

' number of openings -ll through which .the liu-lgs incidental tothellolowing of ,controllecharge freely into the surrounding atmosphere.Cap functions as a receptacle to catch the detached fuse parts whichdrop down when the fuse blows, and, conjointly with ferrule l2, to gripthe flexible leaders of the fuse cartridge and thereby establishelectrical connection between ferrule l2 and the lower terminal of thefusible section, as presently will be described.

The fuse-link assembly comprises cartridge or insert 2 (detailed inFigs. 2, 4, and 5), retracting spring 3, flexible conductors 4, of whichtwo are shown in parallel, and the button-like terminal member The upperend of the cartridge is detachably connected to the lower end of spring3 and to the lower end of conductors 4 through the medium of aconductive member Il.

Fuse cartridge 2 (see Figs. 2, 4, and 5) comprises a metal sleeve |8which is reduced in external diameter at its upper end and externallythreaded at I9 to engage a corresponding internal thread in member l1.This serves to anchor the upper end of the cartridge to member and, inturn, to spring 3 and iiexible conductors Il. Sleeve i8 is internallythreaded at 20 to engage a non-conductive tube 2| which may be made ofhorn ber; and said sleeve has an internal shoulder at |8a whichco-operates with the upper end of tube 2| to grip the external iiange22a of a, metal insert 22 which is bored to form a conically taperedseat for the frustroconical lower end of a sheet metal receptacle orcapsule 23 in which is stored under pressure a suitablearc-extinguishing gas. Capsule 23, which may be a commercial soda waterbottle charging unit lled with carbon dioxide, and commonly known as aSparklet bulb, is held in its seat by means of a metal disc 24 whichpresses against the upper end thereof and is locked in place by ears|82) which are bent over the peripheral edge of the disc. The lower endof capsule 23 is closed by means of a thin metal disc 23a which isadapted to be punctured quickly when subjected to an arc impingingthereon. Puncturing said disc releases the enclosed gas.

Situated immediately below insert 22 and supported on an internalshoulder 2|a formed in tube 2| is a nozzle member 25 having a. borewhich is conically ared at 25a and straight at 25h. The straight portionof the bore is diametrically constricted, as shown, in order to form aconned passageway immediately below the lower end of capsule 23, inwhich passageway the gas discharged from the capsule can be concentratedon the arc which forms when the fuse blows. Sleeve 2i is made,preferably, of refractory, nongas-evolving material such as porcelain orlava The bore diameter at 25h should be smaller than the outsidediameter of the neck forming the lower end portion of capsule 23 so thatthe arc will invariably be concentrated on the aforementioned disc. Ifthe arc is not thus directed, but, instead, is permitted to wander,there may be undue delay or even failure to puncture the receptacle.Hence, the aforementioned bore diameter is a critical factor andconstitutes one of the features of this invention.

Metal insert 22 is slotted externally and axiswise at two diametricallyopposite sides, the slots being identified by reference numerals 22h and22e respectively. Slot 22o receives the upper end of a fuse wire 26,which is soldered in place therein; and slot 22h receives the upper endof a strain wire 27 which similarly is soldered in said slot and isthreaded through an aperture 22d from the bore of insert '22. Sectionalview Fig. 4, considered in conjunction with Fig. 2, shows clearly theslots 22h and 22o and the disposition of strain and fuse wires,respectively, therein. Said strain and fuse wires pass downwardlythrough narrow cross-slots 25d and thence through constricted bore 25hand into the flared passageway 25a, where they are connected at theirlower ends to a solderless compression connector 28. Crossslots 25d areshown most clearly in Fig. 6 wherein the fuse and strain wires have beenomitted for the sake of clarity.

To prevent the fuse and strain wires being twisted there is secured toconnector 28 a washer 28 having oppositely disposed up-turned peripheralears '29a and 29h (see especially Fig. 5) which are seated incorresponding notches 25e formed in the lower end of nozzle member 25.Thus washer 29 is restrained against rotation and, in turn, serves toprevent rotation of connector 28 and the fuse and strain wires.

Attached to connector 28 and depending therefrom are two parallel,stranded, flexible conductive leaders 30, 3| which, as shown in Fig. 1,are intended to be clamped between lower ferrule 2 and lower cap 5-theferrule being slotted at |2a and |22) to provide recesses foraccommodating the flexible leaders.

Normally the fuse cartridge is anchored down in its lowermost positionby the clamping of nexible leaders 30, 3|. This puts spring 3 undertension and, accordingly, biases the cartridge t0- ward movementupwardly, which movement normally is prevented by strain wire 21. Whenthe latter is severed, concurrently with the blowing of the fuse wire,the cartridge is quickly drawn up by spring 3-thereby effecting anabrupt separation of the fuse wire and strain wire terminals and aconsequent stretching out of the arc. Blowing of the fuse wire andincidental severance of the strain wire, as well as the fuse wire, oneither an overload or short circuit causes an arc to form within theconstricted passageway 25h. The upper end of the arc is instantlytransferred to the lower end of capsule 23, and the thin disc 23a isimmediately punctured so that the gas therein is released in the form ofa high velocity jet or blast which impinges directly upon the arc. Allthis occurs within a fraction of a Cycle after the fuse wire blows, andat the same time the arc is being rapidly lengthened by virtue of theupward movement 0f the cartridge. The deionizing effect of the gascoupled with rapid elongation of the arc gap generally results invextinguishing the arc at the first current zero following severance ofthe fuse wire.

an arc, it follows that blowing of the fuse is not accompanied by a loudreport, and no great amount of pressure is developed such as would beapt to burst the cartridge or the housing.

Fiber tube 2| does, no doubt, evolve some gas; but its inside diameteris relatively large and its exposed internal surface is both short andof small area. Hence no great amount of pressure is engendered by reasonof the ber tube. When the fuse has blown and cartridge 2 has movedupwardly under the retractile force of spring there is no mediumintervening the severed ends of the fusible sectionwhich, by reason ofcarbcnization, could presenta substantial lealrage path. This followsYfrom the fact that tube 5, whether of glass or Lucite, is not sus- Ais4made possible by uter to `withdraw ber 11.

power fuses.

receptacle, a lfusible cartridge, one terminal of said fusible sectionbeting attached to said cartridge and the other terminal thereof beinganchored otherwise than 4by.attachment to said cartridgaa springoperaitive to move said cartridge away from the anchorage of said .otherterminal and effective to separate said terminals of said fusiblesection, theigas from said receptacle into the space with- Iinsaidkcartridge traversed by the `arc which results from blowing said fusiblesection, said means Aconcurrently with `nalsiby said spring means.

ceptible to carbonization yand 'provides no conductive surface; Kand theuse of these materials the avoidance of bursting pressures, rlChis is animportant rfeature in a power :fuse and -one vwhich is inherent intheillustrated fuse v`structure and entails Vno `added cost.

-As'willbe self-evid-ent,itis a very simple inatthe entire fuse-linkrfrom the -housing and to detach the cartridge from `mem- Hence,thecartridge can readily bereplaced in the field by Va service man; andthe cost of a replacement cartridge -is a relatively small part of lthecost of the yentire fuse assembly.

*inasmuch as extinguishmentof the arc is not 'dependent uponevolutionofgas, the volume and expulsive action'of which'is predicated upon theintensity of the arc, it follows that an arc of 'lowfcurrentvalue isyextinguished just as readily :as a heavy lcurrent arc; l-has to be madefor extinguishing low-intensity and lno special provision 'arcs as ymust`be done in some other ytypes of Herethe volume of arc-extinguishing gasandthe force of its discharge is constant, irrespective of the intensityof the arc.

What is claimed is:

l. In a fuse, the combination with a fusible section having an anchoredterminal and a movable terminal, of spring means for abruptly moving themovable terminal of said fusible section away from the anchored terminalyupon severance ofrsaid fusible section, a source of arc-extinguishinggas under pressure adjacent the movable terminal land movable therewith,means Aoperative in response to an arc resulting from the severance ofsaid fusible 'section for releas- Ling said -gas immediately adjacentsaid arc concurrently with Athe separation of said terminals vby saidspring means, and a passageway for dilrecting said gases intolthe pathof said arc.

`2. in a fuse, a cartridge including a gas-filled section enclosedwithinsaid abruptly upon severance and vmeans for releasing release thegas as aforesaid the separation of said termib-eing operative to .3, Afuse-link comprising a fusible section,

-means for anchoring one end of said fusible section, spring means forretracting the other end cfsaid yfusible section upon blowing of thefuse whereby abruptly `to elongate the arc which is "formed 4between theterminals of the fusible -sec- Ttion, a source of arc-extinguishing gasunder `)pressure disposed space in which said arc is formed, and meansin operative relation to the responsive to the arc for releasing the gasfrom :said source into said space to assist in the extinguishment .ofsaid arc supplementally to and concurrently with the arc-extinguishingaction vof fsad spring means, said spring biasing said sourcerinzthedirection ofretraction of said other zend.

`4.The combination `in ra fuse-link of a cartridgenclosing a conductive.receptacle filled with" foo /to the lower ends of arc-extinguishing gasunder pressure, 1a kfusible `conductor :disposed within said cartridgeadjafcentone end of said receptacle and sorarranged relative ltheretothat on blowing :of the fusible Iconductor vthe rresultant arc is inseries circuit with said receptacle, oneiendvonly of said fusible`conductor being `anchored toisaid cartridge, the other end of saidfusible conductor being ar- :ranged v to be attached to an anchoragevextraneous Athe fuse-link, the disposition of said fusilole conductorrelatively to said receptacle being such lthatithe arc which results4from blowing of .the fusible `conductor will .quickly puncture saidreceptacle and thus release therefrom a jet of gas directedat-the arc,and a spring for biasing said cartridge toward movement in a directioneffective to separate the severed terminals of vsaid fusible conductorfollowing a blowout.

J5. The combination in a fuse-link of a cart- 4ridgecomprising ametallic sleeve, a tube of insulating material `detachably connected toand depending yfrom said sleeve and co-axial therewith, a removablereceptacle filled with arc-extinguishing gras under pressure disposedvwithin saidsleeveya nozzle member of non-gas-evolving *non-conductivematerial disposed within said vtube immediately below said receptacleand hav- .ing a constricted passageway immediately adja- 'cent the lowerend of said receptacle, a fuse wire one end to the lower ends of saidstrain -`wire and fuse wire, a ytension spring detachably connectedtothe upperend of said cartridge for biasing said lcartridge upwardiy,and means operative in responseto an are resulting from the severance ofsaid fuse wire for releasing said arc extinguish- -ing gas.

6. The combination in a fuse-link of a cartridge lcomprising a metallicsleeve, a retracting spring vdetachably connected to the upper end ofsaid metallicsleeve, a'tube of insulating material `detachably connectedto and depending from the lower end of said metallic sleeve and co-axialtherewith, a metallic insert within said cartridge Aand secured betweensaid sleeve and tube jointly,

Asaid insert having a conically tapered bore, a gas 50 icontainer withinthe bore of said sleeve and seated at its lower end in the conicallytapered bore of vsaid insert, a nozzle member of non-conductive,non-gas-evolving material disposed within said tube immediately belowsaid metallic insert and having a constricted axial passagewaykimmediately below said gas container, a strain lwire-and a fuse wireeach connected at its upper end to said metallic insert and extendingdownwardly through said constricted passageway, a flexible conductiveleader connected at one end said fuse wire and strain wire andextendingfoutwardly from the lower end o'f said cartridge, a terminalmember attached to the upper end of said spring, a flexible conductor4extending axially through said spring and electrically interconnectingsaid terminal member iwith said metallic sleeve, and means operative invresponse to an arc resulting from the severance of said fuse wire forreleasing said gas immedi- .ately adjacent said arc.

17. The combination in a cartridge, a receptacle .ing gas under`pressure fuse-link of a tubular containing arc-extinguishdisposedwithin said cartridge, a nozzle member made of lsubstantiallynongas-evolving, -non-conductive material having -a constricted axialpassageway immediately adjacent and below said receptacle, a fuse Wireextending through said passageway and anchored at its upper end abovesaid passageway, the lower end of said fuse wire being provided withmeans vfor eiecting anchorage thereof extraneously of said cartridge, aretractile spring connected to the upper end of said cartridge formoving said cartridge lengthwise to eiect abrupt separation of theterminals of the severed fuse Wire when a blowout occurs, and meansoperative in response to an arc resulting from the severance of saidfuse wire for releasing said arc extinguishing gas immediately adjacentsaid arc concurrently with the separation of said terminals by saidspring.

8. The combination in a fuse of structure including a receptaclecontaining arc-extinguishing gas under pressure, said receptacle havinga portion constituting an alternate arc electrode, said portion beingquickly perforable by the arc when caused to operate as an arcelectrode, a fusible element having one terminal only electrielTectingelectrical connection with and for anchoring the other terminal of saidfusible element, said portion being so positioned with respect to theterminals of said fusible element that after a blowout has occurred theshortest arc path is between said portion and said other terminal, andspring means for biasing the terminals of said fusible element apart toeiect abrupt separation thereof when a blowout occurs.

9. The combination in a fuse, of a tubular cartridge, a receptaclecontaining arc-extinguishing gas under pressure, said receptacle beingdisposed within said cartridge, a conductive member situated within saidcartridge and bored axially to form a seat for said receptacle, thelower portion of said receptacle projecting downwardly through andbeyond said conductive member, a non-conductive member situated belowsaid receptacle and said conductive member and having a constricted borewhich is obstructed at one end by the lower end of said receptacle, afuse Wire and a strain wire in parallel and each connected spouse to anarc resulting from the severance of said fuse wire for releasing saidarc extinguishing gas immediately adjacent said arc.

l0. The combination in a fuse, of a tubular transparent housing, and atensioned fuse-link within said housing and comprising a tensioned coilspring and a fuse said metallic sleeve and containing arc-extinguishinggas under pressure, said receptacle being generally cylindrical in formand having an attenuated neck portion at one end which seats in saidfrustro-conical bore and projects through and beyond said consaid tubeand immediately adjacent said conductive member, said nozzie memberhaving a constricted bore terminating at one end immediately adjacentthe end of said neck portion, a fuse wire and a strain Wire in parallel,each connected at one end to said conductive member and extendingthrough said constricted bore, a flexible conductive leader connected tothe other ends of said fuse and strain wires, said leader being anchoredto said housing and serving conjointly with said strain wire to maintainsaid fuse-link under tension and means operative in response to an arcresulting from the severance of said fuse Wire for releasing said arcextinguishing gas.

l1. In a fuse, the combination with a fusible section having an anchoredterminal and a movable terminal, of spring means for abruptly moving themovable terminal of said fusible section away from the anchored terminalupon severance of said fusible section, a source of fluidarcextinguishing material under pressure adjacent the movable terminaland movable therewith, means operative in response to an arc resultingfrom the severance of said fusible section for releasing said materialimmediately adjacent said arc concurrently with the separation of saidterminals by said spring means, and a passageway for directing said arcextinguishing material into the path of said arc.

with said sleeve metal insert disposed within one end portion of saidsleeve and co-axial with said sleeve, said insert being secured in placeby said tube and removable from said sleeve after detaching said tubefrom said sleeve, said insert forming, in conjunction with the bore ofsaid sleeve, a chamber, a gas-nlled capsule disposed within saidchamber, said insert being bored through axially provide a seat for oneend of said Way, and means operative in response to an arc resultingfrom the severance of said fusible member for releasing said gasimmediately adjacent said arc.

non-conductive material co-axial with and in end-to-end threadedengagement within a chamber said insert, the latter being bored to forma seat each at one end, respectively, to said insert and at their'otherends to said conductive leader, said wires extending through saidconstricted passageway, and means operative-in response to an arcresulting from the severance oi said fuse wire for releasing saidgasimmediately adjacent said arc.

14. A fuse cartridge constituting a replaceable componentv of afuse-link and comprising: agasfilled capsule, aA conductive sleeve boredlengthwise to form a chamber for'the reception of said capsule, a discsecured in one end of said bore and in pressing engagement with one endof said capsule, a metal insert removably seated within said sleeveremotely from said disc and forming one terminus of said chamber, saidinsert being bored to form a seat for said capsule and to form apassageway through which the other end of said capsule projects, a tubeof non-conductive material co-axial with and in end-to-end threadedengagement with said sleeve, and detachable therefrom, said insert beingclamped in place by said sleeve and tube conjointly, means within saidtube defining a constricted passageway in direct communication with saidother end of said capsule, a conductive leader, a fuse wire and a strainwire, said wires being connected each at one end, respectively, to saidinsert and at their other ends to said conductive leader, said wiresextending through said constricted passageway, and

means operative in response to an arc resulting from the severance ofsaid fuse wire for releasing said gas immediately adjacent said arc.

15. A refill fuse link -unit for fuse cartridges, said unit comprising ametal sleeve having terminal connecting means at one end, an insulatingsleeve secured to and projecting from the other end of said metalsleeve, the end of said insulating sleeve remote from said metal sleevebeing open, a receptacle in said metal sleeve containing 'a fluid underpressure and having a destructible seal in said insulating sleeve forreleasing said fluid, means retaining said receptacle in said metalsleeve, a fusible section electrically connected at one end to saidmetal sleeve and positioned in said insulating sleeve, a flexible leaderconnected with .the other end of said fusible section and projectingfrom the open end of said insulating sleeve, andmeans operative inresponse to an arc resulting from the severance of said fusible sectionfor destroying said seal and releasing said fluid.

16. A refill fuse link unit for fuse cartridges, said unit comprising ametal sleeve having terminal connecting means at one end, an insulatingsleeve secured to and projecting from the other end of said metalsleeve, said insulating sleeve being open at its end remote from saidmetal sleeve and having a nozzle like constriction flaring toward saidopen end, a receptacle in said metal sleeve containing a iiuid underpressure and having a destructible seal adjacent said nozzle likeconstriction, a fusible section electrically connected at one end tosaid metal sleeve and projecting through said constriction, a terminalconnecting conductor projecting from said open end and secured to theother end of said fusible section, and means operative in response to anarc resulting from the severance of said fusible section for destroyingsaid seal and releasing said fluid.

17. An arc extinguishing unit comprising a metal sleeve having aterminal connecting means at one end, an insulating sleeve secured toand projecting from the other end of said metal sleeve, a receptacle insaid metal sleeve containing a fluid under pressure and having adestructible seal in said insulating sleeve for releasing said fluid,means retaining said receptacle in said metal sleeve, and conductormeans extending from said` open end for establishing an arc to saiddestructible seal on the occurrence of an abnormal condition in anelectric line to which said unit may be connected.

i8. An arc extinguishing unit comprising a metal sleeve having terminalconnecting means at one end, an insulating sleeve secured to andprojecting from the other end of said metal sleeve, said insulatingsleeve being open at its endy remote from said metal sleeve and having anozzle-like constriction flared toward said open end, a receptacle insaid metal sleeve containing a fluid under pressure and having adestructible seal adjacent said nozzle-like constriction, and conductormeans extending from said open end for establishing an arc to saiddestructible seal on the occurrence of an abnormal condition in anelectric line to which said unit may be connected.

19. In a fuse, a cylindrical receptacle containtaining arc-extinguishingfluid under pressure, said receptacle having a neck portion of reduceddiameter at one end, the terminus of said neck portion being closed bymeans of a closure member or" thin sheet metal, the exposed diameter ofwhich is less than the outside diameter of said neck portion, a nozzlemember oi non-conductive material having a recess for the reception ofsaid neck portion and a passageway co-axial with said recess andterminated at one end by said closure member, said passageway having adiameter not materially greater than the exposed diameter oi saidclosure member, and a fusible member extending axially through saidpassageway and operative, on blowing, to strike an arc within saidpassageway adjacent said closure member, the arrangement being such thatthe arc will impinge upon said closure member in preference to otherparts of said receptacle, thereby ensuring that said closure member willbe quickly punctured.

20. In a fuse, a nozzle member of non-conductive material having apassageway therethrough, a receptacle containing arc-extinguishing gasunder pressure, said receptacle having a discharge port which isnormally closed by a closure member of conductive material which iscapable oi being quickly punctured by an arc impinging thereon, saidpassageway being terminated at one end by said closure member, saidpassageway being of a diameter, immediately adjacent said closure, notmaterially greater than the exposed diameter of said closure member, andfusible means capable of producing an arc within said passageway, thearrangement being such that said closure member will function as oneelectrode of said are immediately after the' arc is established.

21. An arc extinguishing unit comprising a metal sleeve having aterminal connecting at one end, an insulating sleeve secured to andprojecting from the other end of said metal sleeve, a receptacle in saidmetal sleeve containing a fluid under pressure and having a destructibleelectrically conductive seal in said insulating sleeve for releasingsaid fluid, and a bored metal insert retaining said receptacle in saidmetal sleeve, in combination with a conductor including a fusiblesection adjacent the seal extending from said ,insert through the openend of said insulating 11 sleeve for establishing an arc to saiddestructible seal on the occurrence of an abnormal condition in anelectric line to which said unit may be connected. WILLIAM D. KYLE, JR.ANTHONY VAN RYAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Name Date Eveleth Mar. 20, 1906 Number NumberNumber

